1. Field of the Invention
The present invention relates to a particle holding sheet, a method of manufacturing the particle holding sheet and an organic EL (ElectroLuminescent) display having the particle holding sheet, and more particularly, relates to an moisture absorbent sheet, a method of manufacturing the moisture absorbent sheet and an organic EL display, suitable for removing moisture in a sealed space using an moisture absorbent as a particle when the organic EL elements are hermetically sealed by adhering a substrate on which organic EL elements are formed to a seal cap in the organic EL display. Hereafter, the present invention will be explained using the moisture absorbent sheet and the organic EL display having the moisture absorbent sheet, however, particles are not limited to the moisture absorbent in the present invention.
The present application claims priority of Japanese Patent Application No. 2001-111948 filed on Apr. 10, 2001, which is hereby incorporated by reference.
2. Description of Related Art
An organic EL (ElectroLuminescent) display element has a structure in which a luminescent layer made of an organic compound is put between an anode and a cathode. By applying a direct voltage to the anode and the cathode of the organic EL display element, holes injected from the anode and electrons injected from the cathode are recombined in the luminescent layer to make an excitation state. Then, luminescence occurs in a relaxation process from the excitation state to a ground state.
The organic EL display has good characteristics which cannot be provided by a liquid crystal display, for example, the organic EL display can be a self-luminescent thin flat display with a rapid response ability and a wide angle of visibility.
However, since the organic EL element deteriorates by moisture infiltration, a sufficient lifetime can not be obtained. For example, with the moisture penetrating an interface between the luminescent layer and an electrode, the electrons are prevented from injecting. Therefore, a display quality is deteriorated since a dark spot which is a non-luminescent area generates in the luminescent layer, the electrode corrodes and the dark spot grows to reduce the luminescent area.
Therefore, it is considered that influences of the moisture and a like are prevented by hermetically sealing the organic EL element. For example, an organic EL display is proposed in which the organic EL element is enclosed in a container having no moisture permeability with nitrogen gas and moisture absorbent.
An organic EL display 101, as shown in FIG. 14, is provided with a transparent insulating substrate 102 such as a glass substrate, an anode layer 103, an organic EL lamination body 104 including a luminescent layer, a cathode layer 105 and a seal cap 106. A moisture absorbent 107 is stored in a concave portion 106a formed in the seal cap 106.
The anode layer 103 is formed on the transparent insulating substrate 102 and is made of transparent conductive material such as ITO (Indium Tin Oxide).
The organic EL lamination body 104, for example, as shown in FIG. 14, includes a hole transport layer 108, a luminescent layer 109 and an electron transport layer 110, in that order, on the anode layer 103.
The hole transport layer 108 is made of TPD: N,N′-diphenyl-N,N′-di(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine or alike.
The luminescent layer 109 is made of Alq3: tris (8-hydroxyquinolinol) Aluminum. The electron transport layer 110 is made of 3-(4-biphenylyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4-triazole or a like.
The cathode layer 105 is formed on the organic EL lamination body 104 and is made of aluminum or a like.
The seal cap 106 is made of metal material such as stainless steel, glass, or a like and seals the anode layer 103, the organic EL lamination body 104, and the cathode layer 105. The seal cap 106 has the concave portion 106a for keeping the moisture absorbent 107 and is put on the transparent insulating substrate 102 to cover the anode layer 103, the organic EL lamination body 104, and the cathode layer 105 via a seal resin 111.
The moisture absorbent 107 is composed of particles such as BaO and is held by a gas permeable sheet 112 while being kept in the concave portion 106a of the seal cap 106.
A method of manufacturing the organic EL display 101 will be explained.
First, the anode layer 103 such as ITO is formed on the transparent insulating substrate 102 such as a glass substrate by a sputtering technique or a like. On the transparent insulating substrate 102 on which the anode layer 103 is formed, N,N′-diphenyl-N,N′-di(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine) or a like, tris (8-hydroxyquinolinol) aluminum or a like, 3-(4-biphenylyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4-triazole or a like are deposited by an evaporation technique. With these processes, the organic EL lamination body 104 including the hole transport layer 108, the luminescent layer 109 and the electron transport layer 110 is formed.
Then, the cathode layer 105 such as aluminum is formed on the organic EL lamination body 104 by the evaporation technique using a shadow mask.
As shown in FIG. 15A, the seal cap 106 in which the concave portion 106a is formed is prepared, as shown in FIG. 15B, the moisture absorbent 107 is stored in the concave portion 106a of the seal cap 106 and, as shown in FIG. 15C, the moisture absorbent 107 is covered with the gas permeable sheet 112 so as to be held.
The seal resin 111 of an ultraviolet-curable type is coated on a lower end face of a side wall of the seal cap 106 which holds the moisture absorbent 107. Then, under an inert gas atmosphere such as nitrogen gas or argon gas, the seal cap 106 is put on the transparent insulating substrate 102 and a side wall end face 106b of the seal cap 106 is jointed to the transparent insulating substrate 102 via the uncured seal resin 111.
Then, ultraviolet rays are irradiated from the side of the transparent insulating substrate 102 so as to cure the seal resin 111. Therefore, the organic EL lamination body 104 is sealed by the seal cap 106 while being filled with inert gas such as nitrogen gas or argon gas. With these processes, the organic EL display 101 is completed.
However, in the conventional technique, there is a problem in that it takes time to store the moisture absorbent 107 in the step of keeping the moisture absorbent 107 in the concave portion 106a of the seal cap 106.
In other words, since the moisture absorbent 107 is composed of particles which are apt to be electrified. When the moisture absorbent 107 is stored in the concave portion 106a of the seal cap 106, the moisture absorbent 107 flies and overflows. Therefore, there are problems in that it is difficult to store an accurate amount of the moisture absorbent 107 certainly and in that an operation is complicated and it takes a great amount of working time.
Also, since the concave portion 106a for storing the moisture absorbent 107 is formed in the seal cap 106, a thickness of the seal cap 106 is bigger. Therefore, there is another problem in that the organic EL display is prevented from being thin and small as a whole.
Additionally, these problems also occur in a solar battery module or a like which is necessary to have moisture resistance, and therefore are not only limited to the organic EL display.